An ultrasound diagnostic apparatus transmits ultrasound wave generated by array transducers in an ultrasound probe to a subject and displays images based on ultrasound wave reflected from acoustic impedance boundary surfaces. An ultrasound diagnostic apparatus is extensively used in diagnosis of function and conformation of organs because it is easy to acquire diagnostic images.
In the most popular scan technique of the ultrasound diagnostic apparatus, array transducers arranged in a row are driven electrically and ultrasound images are acquired. Recently, a 2-dimensional array probe or a mechanical oscillation 1-dimension array probe can acquire 3-dimensional image data in that it is now possible to obtain volume rendering images or MPR (multi plane reconstruction) images by reconstruction of the 3 dimensional image data. In the ultrasound diagnosis of a heart or a circulatory organ, the 2-dimensional array probe is often used for acquiring real-time 3-dimensional image data.
The 2-dimensional array probe has 2-dimensionally arrayed oscillation elements on a head part of the probe. The number of the oscillation elements (M0) requires several hundredfold the number of M0 in the 1-dimensional array probe. Therefore, for adding received signals from M0 channels, a cable connecting each of the 2-D oscillation elements in the probe and phase match adding unit in the apparatus body becomes very heavy and can seriously impair handing of the probe.
To solve the above-mentioned problem, Japanese patent disclosure (kokai) No 2005-342194 discloses a method in which first phase match adding units for M2 channels (M2<M0) are provided in the probe and M0 oscillation elements are sectionalized in M2 sub-arrays (each of the sub-arrays includes M1 oscillation elements (M1=M0/M2)). The received signals from M1 elements of each sub array are added in the first phase match adding unit and the received signals of M0 channels are bundled together in received signals of M2 channels.
In this manner, the bundled received signals of M2 channels are transmitted to a second phase match adding unit in the apparatus body by a cable for M2 channels. This second phase match adding unit bundles the received signals of M2 channels in 1 channel received signal. In other words, two adding steps at both the probe and the apparatus body decrease the number of channels into the cable and result in improved handling ability of the probe.
By the way, by the electronic scan of the ultrasound diagnostic apparatus that receives ultrasound from a certain direction by controlling time delay or phase delay of return signal received by arrayed oscillation elements, especially in the case that a number of oscillation elements per unit area is a few, the larger the angle of ultrasound transmitting and receiving relative to the normal line is, the lower is the sensitivity of receiving and image quality, resulting in artifacts caused from increased side lobes.
In addition, in the case that the first phase match adding units are provided in the ultrasound probe, delay signals for controlling time delay or phase delay of the first phase match adding units are normally supplied from the apparatus body in chronological order. Therefore, too many oscillation elements arrayed on the probe head make transfer time of the delay signals for the many oscillation elements too long.
For example, a case that 2304 oscillation elements on an X-Y surface composed of 48 elements along each of the X and Y directions is explained below. In a case that delay data for 2304 oscillation elements is serially transmitted at a 80 Hz repetition frequency from apparatus body, more than a 30μ sec transfer time is needed and the repetition cycle (rate cycle) of 3-dimensional ultrasound transmitting and receiving must be increased to accommodate the transfer time. In other words, when the first phase match adding unit is provided in the apparatus body, because of the transfer time of a large amount of delay data to the first phase match adding unit, there arises a problem that time resolution of data acquisition and displaying are deteriorated.
On the other hand, to solve the problem, it is possible to increase repetition frequency of transfer or adopt parallel transfer. However these solutions further complicate circuit structure and increase power consumption.